Oracle Logical and Physical Database Structures

 Here we will get to know the clear understanding of Oracle database structures.

First let see what are Oracle databse and Instance?

Oracle database :  set of files that store Oracle data in persistent disk storage .

Database Instance :  set of memory structures that manage database files.

The Logical and physical database structures can be understood as below:

• Segments:  are database objects, a table, a index, rollback segments. Every object that consumes space is a segment. Segments themselves consist of one or more extents.
• Extents:- are a contiguous allocation of space in a file. Extents, in turn, consist of data blocks
• Blocks: are the smallest unit of space allocation in Oracle. Blocks normally are 2KB, 4KB, 8KB, 16KB or 32KB in size but can be larger
   
• Data files:  is a physical file on disk that was created by Oracle Database and contains data structures such as tables and indexes.
• Temp file: is a data file that belongs to a temporary tablespace. The data is written to these files in an Oracle proprietary format that cannot be read by other programs.
  
• Control files: is a root file that tracks the physical components of the database.
  
• Online redo log files: is a set of files containing records of changes made to data.